This invention relates to a vacuum-type circuit interrupter and, more particularly, to a vacuum-type circuit interrupter that comprises disc-shaped contacts primarily of beryllium and has a high continuous current rating that requires thick contact rods for supporting the disc-shaped beryllium contacts.
A vacuum interrupter with disc-shaped contacts of beryllium is able to interrupt exceptionally high currents. But beryllium that is suitable for such duty is quite expensive, and it is therefore important that the disc-shaped contacts be as small as possible in order to limit their cost to a reasonable value. In this respect, each contact should be thin and of a relatively small diameter. This presents a problem when dealing with a vacuum interrupter rated for high continuous currents (e.g., in the neighborhood of 3,000 amperes), which have thick contact rods for supporting the disc-shaped contacts. These thick contact rods may have a diameter greater than half that of the associated disc-shaped contact.
The above referred-to problem is that when an arc is formed between the contacts during a high current interruption, there is a tendency for an arc root to run off its associated contact and onto the thick contact rod supporting the contact, which rod is typically of some metal other than beryllium. Such an occurrence can seriously detract from the interrupting capacity of the interrupter because the arc root will vaporize material of the contact rod, causing metal vapors other than beryllium to enter the arc plasma. The presence of such extraneous vapors diminishes the interrupting capacity of the beryllium-contact interrupter.